Finding the Sweet Spot

glycemic index

By David McLaughlin

Our parents tell us: “An apple a day keeps the doctor away.”

A kid in the schoolyard can usually get a laugh reciting: “Peas porridge hot, peas porridge cold, peas porridge in the pot nine days old.”

These phrases may stick in the mind because they rhyme, but they’re worth remembering the next time you sit down to eat. Legumes and many fruits rank highly for health benefits, according to the glycemic index developed in the early 1980s by David Jenkins and his team, including Thomas Wolever and Alexandra Jenkins.

Jenkins is a Professor in the Departments of Nutritional Sciences and Medicine at the University of Toronto and a Scientist in the Keenan Research Centre of the Li Ka Shing Knowledge Institute at St. Michael's Hospital. His research challenged the prevailing wisdom about what people should eat.

Prior to Jenkins’ breakthrough, health professionals generally advised people with diabetes to avoid simple carbohydrates and manage portion sizes to control their condition. However, the diet did not always work for everyone. Jenkins and his colleagues questioned the convention that simple carbohydrates are bad and complex carbohydrates are good.

They fed their research subjects particular foods and measured the change in their blood sugar. It was a shock to nutritionists and doctors that white bread, for example — a complex carbohydrate — caused a significant rise in blood sugar that was comparable to or even higher than the result of eating some sweet treats, such as ice cream.

Next, the researchers created easy-to-understand rankings that showed how certain foods impact blood sugar levels. The top score is 100, assigned to pure glucose. The closer a food comes to 100, the more you should think twice about eating it often. A food high in the glycemic index breaks down quickly, causing a spike in blood sugar. Foods low on the glycemic index take longer to break down, resulting in a slow, steady rise in blood sugar.

Today, diabetes associations in many countries recommend low glycemic index diets to manage diabetes, and new science is showing how the index can help with many chronic illnesses. Jenkins and other researchers have found that foods low on the glycemic index, such as whole wheat pasta, dried legumes and nuts, can also lower the risk of heart disease and may help prevent cancer.